Field of the Invention
The present invention relates to a dispersion-shifted fiber used as an optical transmission line in a wavelength division multiplexing (WDM) transmission system.
Description of the Related Art
A WDM transmission system using an optical fiber network is capable of transmitting a large capacity of information over a long distance. The WDM transmission system typically includes a transmitter that transmits multi-wavelength optical signals, an optical fiber through which the optical signals propagates, a receiver that receives the optical signals, and an optical amplifier that amplifies the optical signals. In such a WDM transmission system, attempts have been conducted to increase the transmission capacity by broadening the wavelength bandwidth of the optical signals.
An optical fiber intended for broadening the wavelength bandwidth has been disclosed (for example, see U.S. Pat. No. 6,282,354). The optical fiber has a zero dispersion wavelength in the range between 1575 nm and 1595 nm, a mode field diameter of 7.9 μm to 9.1 μm, a dispersion slope of not more than 0.10 ps/nm2/km, a cutoff wavelength of not more than 1500 nm, and a transmission loss of not more than 0.203 dB/km at the wavelength of 1550 nm. Further, according to an embodiment of the optical fiber, the dispersion slope value is 0.07 to 0.08 ps/nm2/km (see Table 5 of U.S. Pat. No. 6,282,354).
On the other hand, the wavelength bandwidth that gives an appropriate gain in an optical fiber amplifier has been a subject of intense research in recent years. As a result, it is now possible to amplify the optical signals in a wavelength range between 1530 nm and 1625 nm. However, the optical fiber disclosed in the U.S. Pat. No. 6,282,354 is intended for optical signals in a wavelength range between 1525 nm and 1565 nm, and therefore, it is not suitable for using in a longer wavelength range between 1565 nm and 1625 nm.